Color constancy in digital imagery

Color casts occur in all forms of digital color imagery. Although they usually arise from a mismatch between the chromaticity of the scene illumination and the illumination for which the imaging system was color balanced some situations provide more of a challenge for color constancy methods than others. In the case of digital cameras, for example, the spectral sensitivity of the camera can be measured and hence taken into account when color balancing its images. Also the camera data can be linearized. On the other hand, for digitally scanned film many things are likely to be unknown, including film type, film dye lot, spectral response of the film, film exposure, and film nonlinearity. In addition, many of the relevant scanner characteristics may be hard to ascertain. For an image obtained on the Web, generally nothing is known about its origin; nonetheless, a human observer will quickly notice any error in color balance. This paper discusses the problems of correcting the color in digital color images of various origins and the color constancy methods developed in response to them